New Zealand will mourn the death of Queen Elizabeth II with a one-off public holiday on September 26.

The public holiday would be called "Queen Elizabeth II Memorial Day" and legislation would be passed next week to bring the holiday into force.

Prime Minister Jacinda Ardern said a State Memorial Service for the Queen would also be held in the Wellington Cathedral of St Paul on the same day.

The event will be televised and livestreamed.

"As New Zealand's Queen and much loved Sovereign for over 70 years, it is appropriate that we mark her life of dedicated public service with a State Memorial Service and a one-off public holiday," Ardern said.

"Queen Elizabeth II was an extraordinary person, and I know many New Zealanders will appreciate the opportunity to both mark her death and celebrate her life."

Ardern said the public holiday allowed people to pay their respects and for communities around the country to come together and pay tribute with local events.

"The decision to hold a one-off Public Holiday in the Queen's honour is also in line with similar holidays in the UK and Australia, and is in keeping with what is an historic event."

Ardern confirmed she, alongside the Governor General, would represent New Zealand at the Queen's funeral in London, departing New Zealand on September 14.

Further details on Ardern's travel would be released in coming days.

The death of the Queen was announced on Friday (NZT) and her funeral will be held at Westminster Abbey on Monday, September 19.

A period of national mourning started immediately after the Queen's death was announced and will continue until the date of the National Memorial Service.

Ardern previously said New Zealand's memorial service would be held at some point after the funeral in the UK - and turned its mind this afternoon to setting the date when it meets today as well as whether to have a public holiday.

A one-off national public holiday has been confirmed in Australia on September 22. Prime Minister Anthony Albanese the move was "in honour of the life and service" of the late Queen and would coincide with a memorial service.

BusinessNZ chief executive Kirk Hope told RNZ's Morning Report businesses had already suffered losses from the pandemic and the government had to be careful when making a call that would impose more costs on local businesses.

"Certainly I don't think there's any problem with a memorial, I think there'll be a lot of people who will be wanting to attend that but to add another public holiday, as I said, at a time when many businesses have struggled is a bridge too far."

Even a half-day public holiday would still be costly for businesses, he said.

"We prefer not to have that."

King Charles has announced the day of the Queen's funeral - September 19 - would be a bank holiday in the UK.